Chronic beryllium disease (CBD) is characterized by granulomatous inflammation and progressive fibrosis in the lung. The disease is caused by exposure to beryllium in the workplace, and it continues to be a major public health concern with an estimated 800,000 exposed individuals currently at risk. Considerable evidence indicates that CD4+ T cells are central to the pathogenesis of CBD and that disease is associated with the accumulation of beryllium-specific CD4+ T cells in the target organ. The major goal of the studies in this application is to elucidate the mechanism by which pathogenic CD4+ T cells recognize beryllium in CBD. Previous studies of CD4+ T cells in the lungs of CBD patients have shown large oligoclonal expansions of beryllium-specific T cells that produce Th1-type cytokines. Pathogenic subsets of beryllium-specific T cells in individual patients and among different patients were noted to express the same related T cell receptors (TCRs). Other studies have demonstrated that presentation of beryllium to pathogenic CD4+ T cells is dependent on particular alleles of HLA-DP, and the DP alleles that present beryllium match those implicated in disease susceptibility. The basis for the unusually strong T cell response elicited by beryllium and how it relates to these findings is unclear. Studies in the current application will test the hypothesis that the dramatic response to beryllium in CBD relates to TCR interactions with multiple widely expressed sets of beryllium presenting HLA-DP-peptide complexes. Studies in the first specific aim will define the sequence and motif of peptides that bind to HLA-DP2 and that allow recognition of beryllium by antigen-specific TCRs. The peptide sequences and motifs will be used to identify and verify prevalent self-peptides and proteins that are likely to mediate recognition of beryllium. In separate studies, lung T cells that respond to the different peptide sets will be characterized in regard to TCR expression to understand whether each DP2- peptide/beryllium complex induces distinct or broadly overlapping subsets of responding T cells. Additional studies will determine whether fluorescent DP2-peptide/beryllium multimers ("tetramers") can be used to identify and characterize beryllium-reactive T cells in the lungs and peripheral blood of patients with CBD. Studies in the final aim will determine why only certain HLA-DP alleles seem to be capable of presenting beryllium and whether presentation is limited to DP. Together, these studies will provide new insight into the immunopathogenesis of CBD as well as important information for other CD4 + T cell mediated diseases.